1. Field of the Invention
The present invention relates to a brightness improving structure for a light-emitting module with an optical thin-film surface layer, which can notably improve the brightness of the light-emitting module at high reflectance and transmittance by spacing a light-emitting part of the light-emitting module and a reflective layer of a transparent envelop of the light-emitting module at a certain interval in a concentric circle relationship.
2. Description of the Prior Arts
There are many kinds of light-emitting modules known in the art, such as a daylight lamp, a fluorescent tube or the like. The fluorescent tube is mainly provided with a transparent envelop having an inside wall fully coated with a fluorescent layer. The inside of the envelop is filled with electrically excited lighting gases such as mercury and argon gas, or xenon and neon etc. mercury-free gas. When powered by a high voltage the gases inside of the envelop are excited and emit ultraviolet light. The ultraviolet light then hits the fluorescent layer and is excited into visible light. The visible light then emits outwardly through the fluorescent layer and the transparent envelop. However, in operation, since the inner wall of the fluorescent layer of this kind of light-emitting module is firstly excited into the brightest region by the ultraviolet light, it is necessary for the visible light to travel through the thickness of the fluorescent layer itself for further use. The fluorescent layer can more or less convert ultraviolet light into visible light, but it is a poor material for visible light to transmit therethrough. As a result, luminous efficiency is very low. In general, the coated fluorescent layer is made as thin as possible to improve the light transmittance, but this causes the ultraviolet light to be insufficiently absorbed. The person skilled in the art usually needs to compromise between the high transparency of the fluorescent layer and the sufficient absorption of the ultraviolet light and find an optimum point. The transparency of organic fluorophor is generally higher than that of inorganic fluorophor, but the duration of the former is shorter than that of the later. Thus the inorganic fluorophor is generally used for luminous application. Accordingly, the aforementioned low luminous efficiency defect has not been solved till now.
Further, even if the product is under an optimal operation condition the brightness of the visible light at the fluorescent inner layer will attenuate more than a half when passing through the wall thereof to the outer layer (as shown in FIG. 24). The effect of the fluorescent layer on the visible light transmittance will be simply clarified by the following experiment: place an unlighted fluorescent tube before a lighted one and then compare the brightness before shielding by the unlighted fluorescent tube and that after shielding by the unlighted fluorescent tube, you will find that the brightness after shielding is considerably lowered.